1 files changed, 58 insertions, 0 deletions
diff --git a/library/std/src/sys/common/small_c_string.rs b/library/std/src/sys/common/small_c_string.rs
new file mode 100644
index 000000000..01acd5191
--- /dev/null
+++ b/library/std/src/sys/common/small_c_string.rs
@@ -0,0 +1,58 @@
+use crate::ffi::{CStr, CString};
+use crate::mem::MaybeUninit;
+use crate::path::Path;
+use crate::slice;
+use crate::{io, ptr};
+
+// Make sure to stay under 4096 so the compiler doesn't insert a probe frame:
+// https://docs.rs/compiler_builtins/latest/compiler_builtins/probestack/index.html
+#[cfg(not(target_os = "espidf"))]
+const MAX_STACK_ALLOCATION: usize = 384;
+#[cfg(target_os = "espidf")]
+const MAX_STACK_ALLOCATION: usize = 32;
+
+const NUL_ERR: io::Error =
+    io::const_io_error!(io::ErrorKind::InvalidInput, "file name contained an unexpected NUL byte");
+
+#[inline]
+pub fn run_path_with_cstr<T, F>(path: &Path, f: F) -> io::Result<T>
+where
+    F: FnOnce(&CStr) -> io::Result<T>,
+{
+    run_with_cstr(path.as_os_str().bytes(), f)
+}
+
+#[inline]
+pub fn run_with_cstr<T, F>(bytes: &[u8], f: F) -> io::Result<T>
+where
+    F: FnOnce(&CStr) -> io::Result<T>,
+{
+    if bytes.len() >= MAX_STACK_ALLOCATION {
+        return run_with_cstr_allocating(bytes, f);
+    }
+
+    let mut buf = MaybeUninit::<[u8; MAX_STACK_ALLOCATION]>::uninit();
+    let buf_ptr = buf.as_mut_ptr() as *mut u8;
+
+    unsafe {
+        ptr::copy_nonoverlapping(bytes.as_ptr(), buf_ptr, bytes.len());
+        buf_ptr.add(bytes.len()).write(0);
+    }
+
+    match CStr::from_bytes_with_nul(unsafe { slice::from_raw_parts(buf_ptr, bytes.len() + 1) }) {
+        Ok(s) => f(s),
+        Err(_) => Err(NUL_ERR),
+    }
+}
+
+#[cold]
+#[inline(never)]
+fn run_with_cstr_allocating<T, F>(bytes: &[u8], f: F) -> io::Result<T>
+where
+    F: FnOnce(&CStr) -> io::Result<T>,
+{
+    match CString::new(bytes) {
+        Ok(s) => f(&s),
+        Err(_) => Err(NUL_ERR),
+    }
+}